Submerged arc welding system and submerged arc welding method

Abstract

To provide a submerged arc welding system capable of suppressing the occurrence of welding defects even when external characteristics with a large current change amount relative to a voltage change are applied in submerged arc welding.SOLUTION: A welding system A1 for performing submerged arc welding comprises: a welding power supply device 2 that outputs direct current power; a spray device 7 that sprays flux 79 over a welding object W; and a wire feeding device 5 that feeds a welding wire at a constant speed. The welding power supply device 2 switches an external characteristic indicating an output characteristic between a first external characteristic and a second external characteristic which differs from the first external characteristic. The inclination of a characteristic line of the first external characteristic and the inclination of a characteristic line of the second external characteristic are common and equal to or greater than -5 V / 100 A and equal to or less than -0.1 V / 100 A. A switching frequency between the first external characteristic and the second external characteristic is equal to or greater than 1 Hz and equal to or less than 20 Hz. The average current of the output currents of the welding power supply device is equal to or greater than 300 A.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a submerged arc welding system for performing submerged arc welding and a submerged arc welding method. [Background technology]

[0002] Submerged arc welding has been known for some time. In submerged arc welding, granular flux is spread on the workpiece, a welding wire is fed into the flux, and an arc is generated between the tip of the welding wire and the workpiece to perform welding. In submerged arc welding, a large current is passed through a large diameter welding wire, thereby enabling high efficiency welding of thick plates.

[0003] In submerged arc welding, when controlling the arc length by controlling the external characteristic, there is a problem that the wire melting amount is difficult to change with a change in current because the welding wire used is thick and has a small electrical resistance. For this reason, an external characteristic (constant voltage characteristic with a gentle slope of the characteristic line) in which the current change amount relative to the voltage change is quite large is applied. Patent Document 1 discloses that in the leading electrode of multi-electrode one-sided submerged arc welding, the power supply method is DC, the external characteristic is a constant voltage characteristic, and the speed control method for the wire feed speed is constant speed control. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-83234 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the above external characteristics, a small change in voltage causes a large change in current, and if the current change is too large, the voltage changes in the opposite direction, and this is repeated, which can cause current-voltage oscillation. When this oscillation occurs, the molten pool vibrates at an unstable frequency of about 10 Hz, which can easily lead to welding defects.

[0006] The present invention has been devised in light of the above-mentioned circumstances, and has an object to provide a submerged arc welding system that can suppress the occurrence of welding defects even when an external characteristic in which the amount of current change relative to a voltage change is large is applied in submerged arc welding (the external characteristic is a constant voltage characteristic). [Means for solving the problem]

[0007] A submerged arc welding system provided by a first aspect of the present invention is a submerged arc welding system for performing submerged arc welding, comprising a welding power supply that outputs DC power, a spraying device that sprays flux on a workpiece, and a wire feeding device that feeds welding wire at a constant speed, wherein the welding power supply switches an external characteristic indicating an output characteristic between a first external characteristic and a second external characteristic different from the first external characteristic, a slope of a characteristic line of the first external characteristic and a slope of a characteristic line of the second external characteristic are common and are -5V / 100A or more and -0.1V / 100A or less, a frequency of switching between the first external characteristic and the second external characteristic is 1Hz or more and 20Hz or less, and an average current of the output current of the welding power supply is 300A or more.

[0008] In a preferred embodiment of the present invention, a difference in an up-down direction between a first characteristic line of the first external characteristic and a second characteristic line of the second external characteristic is 3V or more and 5V or less.

[0009] In a preferred embodiment of the present invention, a change in output current of the welding power supply caused by switching between the first external characteristic and the second external characteristic is 50 A or more.

[0010] In a preferred embodiment of the present invention, the speed at which the wire feeder feeds the welding wire is 0.5 m / min or more and 10 m / min or less.

[0011] A submerged arc welding method provided by a second aspect of the present invention is a submerged arc welding method for performing submerged arc welding in a submerged arc welding system including a welding power supply that outputs DC power, a spraying device that sprays flux on a workpiece, and a wire feeding device that feeds welding wire at a constant speed, wherein an external characteristic that indicates an output characteristic of the welding power supply is switched between a first external characteristic and a second external characteristic different from the first external characteristic, a slope of a characteristic line of the first external characteristic and a slope of a characteristic line of the second external characteristic are common and are -5V / 100A or more and -0.1V / 100A or less, a frequency of switching between the first external characteristic and the second external characteristic is 1Hz or more and 20Hz or less, and an average current of the output current of the welding power supply is 300A or more. Effect of the Invention

[0012] According to the present invention, the welding power supply switches the external characteristic between a first external characteristic and a second external characteristic at a predetermined frequency. By switching the external characteristic, the output current of the welding power supply switches at the predetermined frequency. When the output current increases, the arc pressure increases and the force pushing the molten pool increases, and when the output current decreases, the arc pressure decreases and the force pushing the molten pool decreases, so that the molten pool vibrates at the predetermined frequency. In this way, the submerged arc welding system according to the present invention can vibrate the molten pool at a stable frequency, thereby suppressing the occurrence of welding defects. [Brief description of the drawings]

[0013] [Figure 1] 1A and 1B are diagrams for explaining a welding system according to a first embodiment, where FIG. 1A is a block diagram showing the overall configuration of the welding system, and FIG. 1B is a block diagram showing the internal configuration of a welding power supply. [Diagram 2] FIG. 4 is a diagram showing an example of a characteristic line of an external characteristic set by a control circuit. [Diagram 3] 5 is a timing chart for explaining switching of an output current of a welding power supply. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0015] [First embodiment] Fig. 1 is a diagram for explaining a welding system A1 according to a first embodiment. Fig. 1(a) is a block diagram showing the overall configuration of the welding system A1. Fig. 1(b) is a block diagram showing the internal configuration of a welding power supply 2.

[0016] The welding system A1 is a welding system for performing submerged arc welding. As shown in FIG. 1(a), the welding system A1 includes a control device 1, a welding power supply device 2, a welding torch 3, a carriage 4, a wire feeder 5, a wire reel 6, a spreader 7, and an electrode 8. The welding system A1 causes the spreader 7 to spread granular flux 79 and the wire feeder 5 to feed the welding wire into the flux 79 while moving the carriage 4 along the welding line of the workpiece W. The welding wire is supplied from the wire reel 6. The welding power supply device 2 converts AC power supplied from a commercial power source P into power suitable for welding and outputs it, and generates an arc between the electrode 8, which is the tip of the welding wire, and the workpiece W inside the flux 79. Welding is performed by the heat of the arc. As a result, welding is performed along the welding line of the workpiece W. Instead of using the carriage 4, the workpiece W may be moved or rotated.

[0017] Welding torch 3 guides the welding wire fed by wire feeder 5 to the welding point. The tip of the welding wire becomes electrode 8 protruding from the tip of welding torch 3. Welding torch 3 has a contact tip (not shown) that is disposed at the tip and is conductive to welding power supply 2. Welding power supply 2 passes a welding current through the welding wire in contact with the contact tip. Welding torch 3 is fixed to cart 4, and moves as cart 4 moves. Note that welding torch 3 may be directly fixed to cart 4, or may be indirectly fixed via an arm or the like.

[0018] The control device 1 performs various controls of the welding system A1. The control device 1 may be a general-purpose computer with a program installed therein for performing various controls of the welding system A1, or may be a dedicated device for controlling the welding system A1. The control device 1 moves the carriage 4 at a predetermined moving speed. The moving speed is set according to the material and thickness of the workpiece W. The control device 1 instructs the spreading device 7 to start and end spreading of the flux 79. The spreading device 7 may start and stop spreading of the flux 79 manually. The control device 1 instructs the wire feeder 5 to start and stop feeding the welding wire and the feeding speed of the welding wire. In this embodiment, the control device 1 causes the wire feeder 5 to feed the welding wire at a constant speed. The feeding speed is set according to the set welding current, etc., and is not limited to, but is 0.5 m / min or more and 10 m / min or less. The control device 1 also instructs the welding power supply 2 to start and stop power output.

[0019] Welding power supply 2 converts AC power supplied from commercial power source P into desired power and outputs it. In this embodiment, welding power supply 2 outputs DC power. As will be described later, the magnitude of the output current of welding power supply 2 changes at a predetermined frequency. As shown in FIG. 1(b), welding power supply 2 includes a rectifying and smoothing circuit 21, an inverter circuit 22, a transformer 23, a rectifying and smoothing circuit 24, a current sensor 26, a voltage sensor 27, and a control circuit 28.

[0020] Rectifying and smoothing circuit 21 converts AC power input from commercial power source P into DC power and outputs it. Inverter circuit 22 converts DC power input from rectifying and smoothing circuit 21 into high-frequency power and outputs it by switching a switching element by a drive signal input from control circuit 28. Transformer 23 transforms the high-frequency voltage output from inverter circuit 22 and outputs it to rectifying and smoothing circuit 24. Rectifying and smoothing circuit 24 converts the high-frequency power input from transformer 23 into DC power and outputs it. Note that the voltage output from rectifying and smoothing circuit 24 (output voltage of welding power supply 2) may be DCEP (direct current electrode positive) in which the potential of output terminal b (connected to the welding wire) is higher than the potential of output terminal a (connected to workpiece W), or may be DCEN (direct current electrode negative) in which the potential of output terminal b is lower than the potential of output terminal a.

[0021] The current sensor 26 detects the output current of the welding power supply 2, and in this embodiment, is disposed on a connection line connecting one output terminal of the rectifying and smoothing circuit 24 and the output terminal a. The output current of the welding power supply 2 detected by the current sensor 26 is substantially equal to the current flowing through the electrode 8. The current sensor 26 outputs a current value signal corresponding to the detected current instantaneous value to the control circuit 28 and the control device 1. The position where the current sensor 26 is disposed is not limited. The voltage sensor 27 detects the output voltage of the welding power supply 2, and in this embodiment, detects the inter-terminal voltage between the output terminal a and the output terminal b. The voltage is substantially equal to the voltage applied between the workpiece W and the tip of the electrode 8. The voltage sensor 27 outputs a voltage value signal corresponding to the detected voltage instantaneous value to the control circuit 28 and the control device 1. The voltage sensor 27 may detect the voltage between the lead wire attached to the welding torch 3 and the lead wire attached to the workpiece W.

[0022] Control circuit 28 is a circuit for controlling welding power supply 2, and is realized by, for example, a microcomputer. Control circuit 28 receives a current value signal from current sensor 26, a voltage value signal from voltage sensor 27, and various command signals and various set values ​​from control device 1. Control circuit 28 outputs a drive signal to inverter circuit 22.

[0023] When the control circuit 28 receives a command signal from the control device 1 to start the power output, the control circuit 28 starts outputting a drive signal to the inverter circuit 22, thereby starting the power output. When the control circuit 28 receives a command signal from the control device 1 to stop the power output, the control circuit 28 stops outputting the drive signal, thereby stopping the power output.

[0024] Control circuit 28 controls the output current and output voltage so that the output characteristics of welding power supply 2 become the set external characteristics. The external characteristics are characteristics that show the relationship between the welding current and the welding voltage, and are generally expressed by a characteristic line that shows the characteristics. Control circuit 28 sets the external characteristics by setting an arithmetic expression that simplifies the characteristic line. Control circuit 28 sets, as the external characteristics, so-called constant voltage characteristics, in which the welding voltage does not change much even if the welding current changes. In this embodiment, control circuit 28 sets, as the external characteristics, a first external characteristic and a second external characteristic by switching at a predetermined frequency f.

[0025] 2 is a diagram showing an example of a characteristic line of the external characteristic set by the control circuit 28. The horizontal axis of the diagram indicates a current value I, and the vertical axis indicates a voltage value V. In FIG. 2, a characteristic line X of the reference external characteristic 0 is shown by a solid line, and the characteristic line X of the first external characteristic 1 and the characteristic line X of the second external characteristic 2 The reference external characteristic is the external characteristic that serves as the reference, and the characteristic line X 0 is a straight line with a slope of Kr along which the voltage value V becomes the reference voltage value Vr when the current value I becomes the reference current value Ir. 1 is the characteristic line X 0The line is a straight line obtained by moving the line ΔI upward, with a common slope Kr, and passing through (Ir+ΔI, Vr). The function representing the first external characteristic is given by the following formula (1). The characteristic line X of the second external characteristic 2 is the characteristic line X 0 is a straight line obtained by shifting Ir-ΔI, Vr downward, has a common slope Kr, and passes through (Ir-ΔI, Vr). The function representing the second external characteristic is given by the following formula (2). That is, the control circuit 28 sets the characteristic line of the external characteristic by fluctuating it up and down at a predetermined frequency f. V=Kr (I-(Ir+ΔI))+Vr (1) V=Kr (I-(Ir-ΔI))+Vr (2)

[0026] The slope Kr is not limited, but is -5V / 100A or more and -0.1V / 100A or less in this embodiment. That is, the external characteristic set by the control circuit 28 is such that the voltage drop for a current increase of 100A is 0.1V or more and 5V or less. When the slope Kr is less than -5V / 100A, the amount of current change for a voltage change is small, so the amount of wire melting of a large diameter welding wire is unlikely to change. On the other hand, when the slope Kr is -5V / 100A or more, unstable vibration of the molten pool is likely to occur, but in this embodiment, the external characteristic can be switched to make the vibration of the molten pool stable, as described later. When the slope Kr is greater than -0.1 / 100A, the amount of current change for a voltage change becomes too large. In addition, ΔI is not limited, but is preferably 25A or more. In addition, the characteristic line X 1 and characteristic line X 2 The difference ΔV in the vertical direction (the difference in voltage value V when the current value I is the same) is not limited, but is preferably 3V or more and 5V or less.

[0027] The control circuit 28 includes, as its functional components, a frequency setting section 281, an external characteristics switching section 282, a target voltage setting section 283, a voltage control section 284, and a drive signal generating section 286.

[0028] The frequency setting unit 281 is a functional configuration for setting a predetermined frequency f, which is a frequency at which the first external characteristic and the second external characteristic are switched. Experiments by the inventors have confirmed that the occurrence of welding defects can be further suppressed when the predetermined frequency f is in the range of 1 Hz or more and 20 Hz or less. Therefore, although there are no limitations, it is desirable for the predetermined frequency f to be 1 Hz or more and 20 Hz or less. The frequency setting unit 281 outputs the predetermined frequency f to the external characteristic switching unit 282.

[0029] External characteristic switching unit 282 is a functional component for switching the output characteristic of welding power supply 2 between a first external characteristic and a second external characteristic. External characteristic switching unit 282 switches between the first external characteristic and the second external characteristic at a predetermined frequency f input from frequency setting unit 281. Specifically, external characteristic switching unit 282 switches between a correction value ΔI for generating a function indicating the first external characteristic and a correction value (−ΔI) for generating a function indicating the second external characteristic at the predetermined frequency f, and outputs the result to target voltage setting unit 283.

[0030] The target voltage setting unit 283 is a functional configuration for setting a target voltage, which is a target value of the output voltage of the welding power supply 2. The target voltage setting unit 283 sets a function indicating an external characteristic based on a preset gradient Kr, a reference voltage value Vr, a reference current value Ir, and a correction value (ΔI or (-ΔI)) input from the external characteristic switching unit 282. The target voltage setting unit 283 sets a function indicating a first external characteristic (the above formula (1)) while the correction value ΔI is input from the external characteristic switching unit 282, and sets a function indicating a second external characteristic (the above formula (2)) while the correction value (-ΔI) is input. That is, the external characteristic set by the target voltage setting unit 283 is switched by the external characteristic switching unit 282. The external characteristic switching unit 282 may switch between (Ir+ΔI) and (Ir-ΔI) at a predetermined frequency f as the current reference value, and output the result to the target voltage setting unit 283. Furthermore, the external characteristic switching unit 282 may switch between the above formula (1) and the above formula (2) at a predetermined frequency f, and set the result in the target voltage setting unit 283.

[0031] Target voltage setting unit 283 sets a target voltage based on a function indicating the set external characteristic and current value I corresponding to the current value signal input from current sensor 26. That is, target voltage setting unit 283 substitutes current value I, which is the output current of welding power supply 2 detected by current sensor 26, into formula (1) or formula (2) above to calculate voltage value V, and sets the calculated voltage value V as the target voltage. Target voltage setting unit 283 outputs the set target voltage to voltage control unit 284.

[0032] Voltage control unit 284 is a functional component for controlling the output voltage of welding power supply 2. Voltage control unit 284 performs feedback control so that the output voltage of welding power supply 2 becomes the target voltage. Specifically, voltage control unit 284 calculates the deviation between the voltage value signal input from voltage sensor 27 and the target voltage input from target voltage setting unit 283. Then, voltage control unit 284 performs calculation using, for example, PI control on the calculated deviation, and outputs the calculated value to drive signal generation unit 286.

[0033] The drive signal generating unit 286 is a functional configuration for generating a drive signal to be output to the inverter circuit 22. The drive signal generating unit 286 generates a drive signal for PWM control, for example, by a triangular wave comparison method, based on a calculated value input from the voltage control unit 284. The drive signal generating unit 286 outputs the generated drive signal to the inverter circuit 22.

[0034] Inverter circuit 22 converts the DC power input from rectifying and smoothing circuit 21 into high-frequency power and outputs it by switching the switching element in response to the drive signal input from drive signal generating unit 286. The high-frequency power is converted into DC power via transformer 23 and rectifying and smoothing circuit 24 and output from welding power supply 2. The relationship between the output current and output voltage of welding power supply 2 corresponds to the external characteristics set in target voltage setting unit 283. The external characteristics set in target voltage setting unit 283 are switched between first and second external characteristics by external characteristic switching unit 282. As shown in FIG. 2, when the output voltage is Vd, and target voltage setting unit 283 uses the first external characteristic (above formula (1)), the output current is I 1 When the target voltage setting unit 283 uses the second external characteristic (the above formula (2)), the output current is I 2 ( 1 In other words, the output current is I 1 and I 2 and are switched at a predetermined frequency f. The average current of the output current of welding power supply 2 is 300 A or more. Furthermore, by setting ΔI to 25 A or more, the change in output current of welding power supply 2 due to switching between the first external characteristic and the second external characteristic is 50 A or more.

[0035] 3 is a timing chart for explaining the switching of the output current of welding power supply 2. Fig. 3(a) shows the change over time of the correction value output by external characteristics switching unit 282. The correction value switches between ΔI and (-ΔI) at a predetermined frequency f. Fig. 3(b) shows the change over time of the output current of welding power supply 2. The output current switches at a predetermined frequency f in response to the switching of the correction value.

[0036] The internal configuration of control circuit 28 is not limited to that described above. Control circuit 28 may control the output current and output voltage so that the output characteristic of welding power supply 2 becomes an external characteristic obtained by switching between the first external characteristic and the second external characteristic at a predetermined frequency f.

[0037] ​Next, the operation and effects of the welding system A1 according to this embodiment will be described.

[0038] According to this embodiment, the welding power supply 2 switches the external characteristic between the first external characteristic and the second external characteristic at a predetermined frequency f. By switching the external characteristic, the output current of the welding power supply 2 switches at the predetermined frequency f. When the output current increases, the arc pressure increases, the force pushing the molten pool increases, and the molten pool is pushed down. On the other hand, when the output current decreases, the arc pressure decreases, and the force pushing the molten pool decreases, so the molten pool tries to return to its original state. Therefore, the molten pool vibrates at the predetermined frequency f. As a result, the welding system A1 can vibrate the molten pool at a stable frequency, so that the occurrence of welding defects can be suppressed. Also, according to this embodiment, the predetermined frequency f is 1 Hz or more and 20 Hz or less. Therefore, the welding system A1 vibrates the molten pool at a frequency of 1 Hz or more and 20 Hz or less. As a result, the welding system A1 can further suppress the occurrence of welding defects.

[0039] In addition, according to the present embodiment, the characteristic curve X of the first external characteristic 1 and the characteristic line X of the second external characteristic 2 The difference in the vertical direction between these is 3 V or more and 5 V or less. Also, the change in output current of welding power supply 2 caused by switching between the first external characteristic and the second external characteristic is 50 A or more. Therefore, welding system A1 can appropriately vibrate the molten pool by the fluctuation in current caused by switching between the first external characteristic and the second external characteristic.

[0040] Furthermore, in this embodiment, the average current of the output current of the welding power supply 2 is a large current of 300 A or more. Therefore, the workpiece W and the welding wire melted by the arc increase, and the vibration of the molten pool becomes more noticeable. Even in this case, the welding system A1 can stably vibrate the molten pool at the predetermined frequency f, thereby suppressing the occurrence of welding defects.

[0041] The submerged arc welding system according to the present invention is not limited to the above-described embodiment. The specific configurations of the components of the submerged arc welding system according to the present invention can be freely designed in various ways. [Explanation of symbols]

[0042] A1 to A2: welding system, 2: welding power supply device, 5: wire feeder, 7: sprayer

Claims

1. 1. A submerged arc welding system for performing submerged arc welding, comprising: a welding power supply that outputs DC power; A spraying device for spraying flux onto the workpiece; a wire feeder that feeds a welding wire at a constant speed; Equipped with the welding power supply switches an external characteristic indicating an output characteristic between a first external characteristic and a second external characteristic different from the first external characteristic; a slope of the characteristic line of the first external characteristic and a slope of the characteristic line of the second external characteristic are common and are −5 V / 100 A or more and −0.1 V / 100 A or less; A frequency of switching between the first external characteristic and the second external characteristic is 1 Hz or more and 20 Hz or less, The average current of the output current of the welding power supply is 300 A or more. Submerged arc welding system.

2. a difference in an up-down direction between a first characteristic line of the first external characteristic and a second characteristic line of the second external characteristic is 3 V or more and 5 V or less; 2. The submerged arc welding system of claim 1.

3. a change in output current of the welding power supply caused by switching between the first external characteristic and the second external characteristic is 50 A or more; 2. The submerged arc welding system of claim 1.

4. The speed at which the wire feeder feeds the welding wire is 0.5 m / min or more and 10 m / min or less.

4. A submerged arc welding system according to claim 1.

5. A submerged arc welding method for performing submerged arc welding in a submerged arc welding system including a welding power supply device that outputs DC power, a flux spraying device that sprays flux on a workpiece, and a wire feeding device that feeds a welding wire at a constant speed, comprising: switching an external characteristic indicating an output characteristic of the welding power supply between a first external characteristic and a second external characteristic different from the first external characteristic; a slope of the characteristic line of the first external characteristic and a slope of the characteristic line of the second external characteristic are common and are −5 V / 100 A or more and −0.1 V / 100 A or less; A frequency of switching between the first external characteristic and the second external characteristic is 1 Hz or more and 20 Hz or less, The average current of the output current of the welding power supply is 300 A or more. Submerged arc welding method.

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